Method of grease manufacture



March 2 9 F. BADGETT ETAL 3,242,082

METHOD OF GREASE MANUFACTURE 2 Sheets-Sheet 1 Filed May 22, 1963 Air mma

L. F. BADGETT ETAL 3,42,U82

METHOD OF GREASE MANUFACTURE March 22, 1966 2 Sheets-Sheet 2 Filed May22, 1963 Q2 w m/ 9 cow United States Patent 3,242,082 METHOD 0!? GREASEMANUFACTURE Lloyd F. Badgett, Port Arthur, William R. Hencke,

Groves, and Fred T. Crookshank, Port Arthur, Tex.,

assignors to Texaco Inc, New York, N.Y., a corporation of Delaware FiledMay 22, 1963, Ser. No. 282,330 7 Claims. (Cl. 25234) This inventionrelates to improvements in grease manufacture and more particularly toan improved low temperature method for the preparation of soap thickenedgreases.

The so-called low temperature methods of grease manufacture comprisesaponifying a saponifiable fatty acid material with a metal base in thepresence of a portion of the lubricating oil employed in the grease,heating the grease mixture at a higher temperature below the meltingpoint of the soap for dehydration and soap conditioning periods, andthen cooling with the addition of the re mainder of the lubricating oilemployed in the grease. These methods have very important advantages inconvenience and economy over the soap melt processes wherein a mixtureof lubricating oil and soap is heated at a high temperature above themelting point of the soap and the mixture then cooled by various means,ordinarily at a rapid rate. However, the low temperature methods havethe disadvantages of generally producing much lower yields than the soapmelt processes and of requiring very long manufacturing times, due bothto the long heating times required to obtain satisfactory yields andproduct quality and to the long cooling times necessitated by theinability of the grease mixture to accept at a rapid rate the additionaloil which is added during the cooling. The present invention provides animproved low temperature process for the preparation of soap thickenedgreases, wherein very large reductions in manufacturing times as well asimproved yields and other advantages are obtained. We obtain theseadvantages by employing a method which comprises essentiallycontinuously recirculating a minor stream of grease mixture through arecycle line from a maintained relatively dilute body thereof in theheating and cooling steps and introducing the oil added during thecooling into the circulating stream of grease mixture, the combinedstream of grease mixture and added oil being subjected to turbulentmixing before it is introduced into the maintained body of greasemixture. Shearing of the recirculating stream of grease mixture may beemployed during the oil addition, and during other steps of the processif desired, very suitably by means of a shear valve located in therecycle line after the point of oil injection.

Grease mixtures prepared in the above manner contain relatively longsoap fibers Which are present in the form of a well-dispersed or looselyagglomerated fiber m-at prior to the cooling step, as shown by electronmicrographs, very differently from the strongly agglomerated soap fibersobtained by the conventional low temperature methods. The method ofadding the additional oil at a lower temperature to a recycle stream ofthe grease mixture during the cooling step has the efiect of partiallywarming the additional oil and mixing it with soap fibers before it isintroduced into the body of grease mixture. The grease mixtures obtainedby the method involving recirculation during the development of the soapfibers are particularly adapted to receive the additional oil added inthis manner at a very rapid rate because of the dispersed or looselyagglomerated condition of the soap fibers. However, this method ofadding the additional oil during cooling may be employed veryadvantageously with grease mixtures obtained by other means also,including the conventional 3,242,082 P e t d Ma 2 1 19.55

low temperature methods and soap melt methods. In the case of greasemixtures prepared by such other methods, it is usually necessary toemploy shearing of the recirculating stream after the oil additionthereto in order to carry out the oil addition at a substantiallyincreased rate.

The preferred embodiment of this invention comprises carrying out thepreparation of the grease mixture with a kettle charge containing only arelatively small amount of lubricating oil and adding preheated oil tothe grease mixture following the saponification and substantialdehydration as a means of obtaining greatly shortened saponification anddehydration times and of heating the grease mixture rapidly to the toptemperature. The amount of oil which is added in this manner issuflicient to give a grease mixture before the cooling step andpreferably during at least a substantial portion of the heating stepcomprising oil and soap in a ratio of at least 1:1, repectively, andmost suitably at least about 4:1, respectively, with greases such ascalcium and lithium hydroxy fatty acid soap thickened greases which aredifiicult to prepare in satisfactorily smooth form. The preheated oil isvery advantageously introduced into the recirculating stream of greasemixture in the same manner as the introduction of oil added during thecooling step.

When operating under our preferred conditions as described herein,grease preparations are carried out with reductions in the manufacturingtime as high as 80 percent or more of the time required by theconventional low temperature procedures, as Well as with improved yieldsand other advantages. The procedure thus offers a means of obtaininggreatly increased grease production with ordinary grease makingequipment by relatively low equipment investments in pumps, heatexchangers and piping. A special advantage of this invention lies in thefact that it provides an answer to the long standing demand in theindustry for a low temperature method of grease manufacture which can becarried out in a single eight-hour work shift.

FIG. 1 is a diagrammatic illustration of one form of apparatus suitablefor making greases in accordance with this invention.

FIG. 2 is a graphic representation of the manufacturing time requiredfor a 10,000 pound batch of a calcium 12-hydroxystearate grease both byconventional plant manufacture and by the method of this invention.

Referring in more detail to FIG. 1, numeral 1 represents a jacketedgrease kettle equipped with stirrer 2 and adapted to be heated to anelevated temperature above about 350 F. In carrying out the greasepreparation, the grease kettle is charged with saponifiable material,lubricating oil, in .an amount equal to about 0.25 to about 10 times theweight of the saponifiable material, and metal base in approximately thestoichiometric amount required to react with the saponifiable material.Ordinarily water is also added to the charge in an amount equal to about0.5 to about 10 times the weight of the metal base. In some cases, wherewater is required to obtain a complete reaction, it is found that areduction in the manufacturing time required may be obtained byemploying a waterfree kettle charge and blowing the reaction mixturewith steam at a temperature above about 200 F. until the saponificationissubst'antially complete. The kettle contents are heated with stirringuntil saponification and dehydration are substantially complete, asshown by the cessation of foaming, and then heated further to a highertemperature to complete the dehydration and to condition the soap.

The maximum temperature to which the grease mixture is heated isordinarily in the range from just below the melting point of the soap toabout F. below the melting point of the soap. In some cases, it may beheated at or even slightly above the melting point of the soap for aperiod which is insuificient to obtain complete melting of the soap. Theheating cycle in the grease preparation ordinarily includes a period ofat least about 15 minutes within the top temperature range, ordinarilyfrom about 15 minutes to about 1 hour. Longer heating periods within thetop temperature range may be einployed although they are generally notnecessary with grease preparations carried out by the method of ourinvention.

During the heating cycle and preferably before the grease mixture hasbeen heated to the maximum temperature, recirculation of the greasemixture around the kettle is begun by turning valves 6 and 8 to the openposition and starting pump 12. The grease mixture passes through line 5,containing valve 6, line 10 containing valve 8, pump 12, and line 14containing pressure gauge 15 and shear valve 19. Lines 5, 10 and 14 maybe jacketed or otherwise provided with means for applyingadditional-heating and cooling to the recirculating stream of greasemixture. The shear valve is suitably a gate valve, which is preferablyin the wide open position at least until dehydration of the greasemixture is substantially complete. Valve 19 is located a sufiicientdistance from kettle 1 to avoid spraying into the kettle when it isoperated under a back pressure, suitably a distance equal to at leastabout 12 times the diameter of pipe 14. As indicated in FIG. 1, therecycle stream of grease mixture is preferably returned at the top ofthe grease kettle, or at least at a point above the surface of the bodyof grease mixture within the kettle. This has the advantage of greatlyincreasing the rate of water evaporation in the dehydration step,thereby very materially shortening the dehydration step, particularlywhere a relatively large amount of water is employed in thesaponification.

Circulation of the grease mixture through the recycle system during theheating cycle following the saponification step is carried out at a ratesufficient to give one batch turnover within about 22 minutes, such asin about 0.3-22 minutes, and preferably in about 0.4-15 minutes, basedon the weight of the grease mixture during the heating cycle, or inabout 0.2515 minutes, and preferably 0.3-12 minutes, based upon theaverage weight of grease mixture during the heating cycle when theprocess is carried out with additional oil added during the heating stepas described hereinbelow. Recycling during the cooling cycle is suitablycarried out at a rate sufficient to provide a batch turnover in about0.535 minutes, preferably in about 1-20 minutes, based on the Weight ofthe finished grease, or in about 0.4-27 minutes, and preferably about-17 minutes, based on the average Weight of grease mixture during thecooling cycle. In general, faster recycling rates in the heating stepresult in smoother products and increased yields, particularly in thecase of lithium and calcium hydroxy fatty acid soap thickened greases.When recycling is employed during the saponification and dehydrationsteps upon a charge containing only a minor amount of the lubricatingoil employed in the grease, recycling rates resulting in a batchturnover in about 0.1-15 minutes, and preferably in about 0.25- minutes,may be employed.

Very advantageously, the recycling is carried out for a minimum periodof about minutes,and preferably for at least about 30 minutes during theheating step following the saponification, until at least 5 batchturnovers and preferably at least 10 batch turnovers, based on theaverage weight of the grease mixture during thisperiod, are obtained. Itis preferably carried out continuously following the saponification andsubstantial dehydration throughout the heating cycle.

Cooling of the grease mixture is carried out by cutting off the heat tothe grease kettle, and to the recycle lines if such additional heatingis employed, and introducing lubricating oil from tank into therecirculating stream of grease mixture. The added oil is at atemperature substantially below that of the grease mixture, such as atleast about F., and preferably at least about F., below the temperatureof the grease mixture at the beginning of the cooling step. Thelubricating oil passes from tank 20 into line 36 by way of line 22containing valve 23, pump 24, line 25 and line 26 containing valve 27,dial thermometer 33, pressure gauge 34 and valve 35. Valve 35 ispreferably a one way valve, most suitably of a type designed to preventgravity flow of oil through pump 24 when the pump is not operating, suchas a diaphragm controlled reducing valve or a spring loaded check valve.In line 36, the oil may pass into the recirculating stream of greasemixture at the intake of pump 12 by passing through valve 37 into line10, or into the grease mixture at the discharge side of pump 12 bypassing through valve 38 into line 14. It is preferably passed into thegrease mixture at the intake side of pump 12 in order to obtainincreased mixing and shearing by the action of the pump, particularlywhen valve 19 is in the wide open position. The oil may be introducedinto the recirculating stream of grease mixture at a rate such that theratio of the rate fo flow of the grease mixture before the point ofconfluence to the rate of oil injection is from about 1:1 to about 400:1, preferably in a ratio from about 2:1 to about 150:1, and mostadvantageously in a ratio from about 3:1 to about 50:1, by weight,respectively. During the oil injection, valve 19 may be in the wide openposition or in a partly closed position, such as to give a pressure dropacross the valve of about 10200 pounds per square inch. It is usuallypreferable to carry out the oil injection With valve 19 in a partlyclosed posit-ion resulting in a pressure drop of about 25-125 pounds persquare inch.

The oil addition is preferably commenced at the beginning of the coolingstep, and may be carried out Over the entire cooling period or throughonly a portion thereof. Additional cooling may be, applied to thekettle, and also to the recirculating stream of grease mixture. Theamount of lubricating oil added during the cooling may amount to fromabout 10 to as high as about 95 percent of the total oil contained inthe grease. It will usually be from about 25 to about 75 percent of thetotal oil contained in the grease. When the oil addition is carried outduring only a portion of the cooling step, it is advantageous in somecases to continue recirculation of the grease mixture with shearing downto the drawing temperature. Any additives employed in the grease areordinarily added during the cooling step when the grease mixture is at asuitably low temperature, generally at below about 250 F. The cooledgrease mixture is finally drawn through line 40 containing valve 41.

The grease mixture before the cooling step preferably comprises oil andsoap in a weight ratio above 1:1, respectively. With greases of the typewhich are difiicult to prepare in satisfactorily smooth form, such aslithium and calcium hydroxy fatty acid soap thickened greases, themixture preferably comprising oil and soap in a weight ratio of at leastabout 421, respectively, andmost advantageously at least about 5 :-1,respectively. Theprocedure which is regarded as the particularlypreferred embodiment of this invention comprises employing only arelatively small amount of lubricating oil in the saponificationmixture, and adding the remainder of the lubricating oil required togive the desired oil-soap ratio at at higher temperature than the greasemixture during the: heating step, preferably following substantialdehydra-- tion of the grease mixture. The preheated oil is very'advantageously introduced into the recycle line of the: grease mixturein the same manner as the oil added. during cooling. tank 20 to heater3!? by way of line 22, pump 24, line; 25 and line 23 containing valve29. Heater 30 may be anysuitable type of heater such as a coil heater asindicatcd in the diagram. From heater 30 the oil passes. into line 26and is introduced into the circulating stream In this procedure, the oilpasses fromof grease mixture at either the intake or the discharge sideof pump 12 as described hereinabove in connection with the introductionof the oil during cooling. It is introduced at the discharge side ofpump 12 when light oils are employed which may cause vapor locking inthe pump. The temperature of the oil added in this manner is preferablysubstantially higher than that of the grease mixture, and may be up toor even slightly higher than the melting point of the soap. The rate atwhich the oil is introduced may suitably be such that the ratio of therate of recirculation of the grease mixture to the rate of oil injectionis within the ranges disclosed hereinabove in connection with theintroduction of cold oil during the cooling cycle. The amount of oiladded in this manner may be from about 5 percent up to about 70 percentof. the total oil employed in the grease. In the preparation of lithiumhydroxy fatty acid soap thickened greases it is preferably not aboveabout 50 percent and most suitably from about to about 30 percent of thetotal oil employed in the grease. A portion of this oil may be addedthrough the kettle top, it necessary, to obtain a grease mixture whichis sufficiently fluid to circulate:

Shearing of the recirculating stream of grease mixture may be carriedout during the addition of the preheated oil by setting valve 19 so asto obtain a pressure drop of about 10-200 pounds per square inch acrossthe valve. Shearing of the grease mixture in this manner may also becarried out very advantageously in some cases during other stages of theheating cycle also, particularly during the heating at top temperature.v

Greases of the types which are ordinarily finished by milling may bemilled in the usual manner, such as by means of a colloid mill set at anarrow clearance. However, the milling step may generally be obviated byshearing during the grease preparation by means of a shear valve in therecycle line as described above. The manner is which this shearing isapplied for optimum results, including both the severtity and durationof the shearing and the stage in the grease making process wherein it isemployed, varies considerably according to the type of grease beingproduced, depending principally upon the character of the soapthickener.

The metal base employed in the saponification may be a hydroxide orother suitable compound of any of the metals ordinarily employed as themetal component of the soap in the preparation of lubricating greases,such as sodium, lithium, potassium, calcium, barium, magnesium, zinc,cobalt, manganese, aluminum, lead, etc., as well as mixtures of two ormore metals. It is preferably a metal oxide, hydroxide. or carbonate.The greases which are most advantageously prepared by the method of thisinvention are those wherein the soap thickener is an alkali metal oralkaline earth metal soap, or a mixture of two or more soaps of theseclasses.

Suitable saponifiable materials for use in these grease preparationscomprise higher fatty acids containing from about 12 to 32 carbon. atomsper molecule and hydroxy substituted higher fatty acids, theirglycerides and other esters and mixtures thereof. The invention alsocontemplates grease preparations carried out in the manner describedabove wherein such higher fatty acid materials are employed inconjunction with lower fatty acid materials, such as fatty actidscontaining from one to about 6 carbon atoms per molecule, theirglyceries and other esters. Such lower fatty acid materials may beemployed in amounts giving a mol ratio of lower fatty acid to higherfatty acid from below 1:1 up to about 20:1, respectively. Also,intermediate fatty acid materials may be employed in conjunction withthe higher fatty acid materials in varying amounts, ordinarily inamounts giving a mol ratio with the higher fatty acid material belowabout 1:1, respectively.

The oleaginous liquids employed in these greases may be any suitableoils of lubricating characteristics, includture up to 260 F. in 10minutes.

utes, and maintained at 280-286 F. for hour.

ing the conventional mineral lubricating oils, synthetic oils obtainedby various refining processes such as cracking and polymerization andother synthetic oleaginous compounds such as high molecular weightethers and esters. The dicarboxylic acid esters, such as di-2ethylhexylsebacate, di(secondary amyl)sebacate, di-Z-ethylhexyl azelate,di-iso-octyl adipate, etc., comprise a particularly suitable class ofsynthetic oils and may be employed either as the sole oleaginouscomponent of the grease or in combination with other synthetic oils ormineral oils. The oil employed in the saponification mixture ispreferably one which is substantially inert under the saponifica tionconditions, most suitably a mineral lubricating oil. Suitable mineraloils for use in these greases are those having viscosities in the rangefrom about to about 2000 seconds Saybolt Universal at 100 F., which maybe blends of lower and higher viscosity oils. They may be eithernaphthenic or parafiinic in type, or blends of two or more oils of thesedifferent types.

The following examples are illustrative of lubricating greasepreparations carried out in accordance with this invention.

Example I A calcium 12-hydroxystearate thickened grease was prepared bythe method of this invention as: described below.

The following materials were employed in the grease preparation: Thelubricating oil employed was a naphthenic distillate oil having aSaybolt Universal viscosity at 100 F. of 58 seconds. The saponifiablematerial employed was a commercial l2-hydroxystearic acid having asaponification number of 187, an acid number of 173 and an iodine numberof 5.

The equipment employed in the grease preparation was a 150 poundcapacity jacketed steam heated laboratory kettle with auxiliaryequipment for grease circulation and hot and cold oil injection as shownin FIG. 1. The grease circulation equipment consisted of 1% inch pipeconnecting the kettle draw-off with a No. 2 Globe Rota Piston pumphaving a capacity of approximately 17 gallons per minute, and a inchpipe extending from the pump to the top of the kettle and containing ashear valve. The pipes were insulated and steam traced. The oilinjection system comprised a 100 pound charge tank, a controlled volumepump having a capacity of approximately 25 gallons per hour and a GrahamHeliflow Exchanger for heating the oil.

Following is a detailed description of the method employed in the greasepreparation: The grease kettle was charged with 33.9 pounds oflubricating oil, 11.30 pounds of IZ-hydroxystearic acid and 1.72 poundsof lime. Stirring and jacket heating of the kettle contents were begun.At the same time recirculation of the kettle contents through therecycle line was begun at a rate of 17 gallons per minute, with theshear valve in the wide open position. After 15 minutes, when thetemperature of the mixture had reached 220 R, an additional 27.6

pounds of lubricating oil preheated to 290 F. were injected into therecycle stream at the intake side of the pump at a rate of pounds perhour with continued kettle heating, which brought the temperature of themix- The kettle contents were further heated to 280 F. in an additional20 min- The heat was then cut off and 26.8 pounds of lubricating oil at78 F. were injected into the recycle stream at a rate of pounds perhour, which resulted in cooling the grease mixture to 236 F. in about 15minutes. Stirring and recirculation of the grease mixture were continuedwhile the grease mixture was further cooled to the drawolf temperatureof F.

The total time required for the above preparation was 2 hours, ascompared with 15.75 hours required for a laboratory preparation of thesame size carried out by the conventional low temperature methodemployed in plant manufacture. The greases obtained by the two methodsstirring for one half hour. cycle line was then discontinued and 48pounds of the distillate oil at 100 F. were introduced into therecirculating stream of grease mixture at the intake side of '7 weregenerally equivalent in appearance and lubricating properties. Thefollowing tabulation shows analyses and tests obtained upon thesegreases.

The time required for preparing a 10,000 pound plant batch of the abovegrease by the recirculation-oil injection procedure described above isabout 4.2 hours, calculated from the laboratory preparation on the basisof heat transfer data obtained on an oil heated plant kettle. On thesame basis, the time required for a 10,000 pound batch in the samekettle by the conventional procedure is about 24.1 hours. A comparisonof the times required for the separate steps of the grease makingprocess by the above method and by the conventional procedure is showndia grammatically in FIGURE 2.

Example II A lithium 12-hydroxystearate thickened grease was prepared bythe method of this invention as described below.

The -following materia'ls were employed in this preparationi The.lubricating oil employed was a blend in about a 7:5.3 ratioby weight,respectively, of a refined Manvel residuum having a Saybolt Universalviscosity at 210 F. of about 107 seconds and a refined parafiinicdistillate "oil having a Saybolt Universal viscosity at 100 F. of about180 seconds. The saponifiable material employed was a commercial methyl12-hydro'xystearate, having a saponification number of 178, aneutralization number of and an iodine number of 3.

The equipment employed in this preparation was the same as thatemployedin the grease preparation described in Example I.

Following is a detailed description of the method employed in the greasepreparationrThe grease kettle was charged with 1.41 pounds of lithiumhydroxide monohydrate, 4.2 pounds of water, 8 pounds of the Manvelresiduum and 8.6 pounds of methyl 12-hydroxystearate.

Stirring and jacket heating of the kettle-contents were begun. Whenthemixture was heated to 140- R, which required about 8 minutes,recirculationof the mixture through the recycle line was begun at a rateof 17 gallons per, minute with the shear valve inwide open position. Atthe same time, introduction of an additional 55.5

pounds of the Manvel residuum preheated to 290 F.

was begun. The preheated oil was introduced into the recycle stream .atthe intake side of the pump at a rate :of 60 pounds per hour duringheating of the grease .mixture to 305 9 F. The grease mixture was thenfurther heated to' about 338 F., the time from the beginning ofrecirculation to the top temperature being 1.5 hours. The grease mixturewas maintained at a temperature in the range 335340 F. with continuedrecirculation and Heating of the kettle and rethe pump at a rate of 60pounds per hour, which resulted in cooling the grease mixture to 200 F.in 45 minutes. The grease was finished by milling with one pass througha Premier Colloid Mill set at 0.003 inch clearance.

The product obtained as described above was a smooth grease of goodappearance and lubricating properties,

x 8 having an ASTM penetration-at,77 F. of 317, unworked,

and 327, worked, for a 6.9 percent lithium-12-'hydroxy stearate content.

The total manufacturing time, aside from the milling step, for the abovepreparation was 2 hours and 50 minutes. This represents a very largesaving in manufacturing time over the times required by the prior artmethods for the preparation of lithium hydroxy fatty acid soap thickenedgreases, including that of W. R. Hen'cke et al. described in US.3,015,624. In addition, applicants process provides yields which are atleast equivalent and generally superior to thoseobtain'ed by the Henckeet a1. process, being greatly superior to those obtained by the olderprior art processes.

Obviously many modifications and variations of the invention, ashereinbefore set forth, may be made without departing from the spiritand scope thereof, and therefore only such limitations should be imposedas are indicated in the appended claims.

We claim:

1. In a low temperature process for preparing a soap thickened greasewhich comprises providing a hot grease mixture comprising a portion ofthe lubricating oil contained in the finished grease and soap dispersedtherein, said grease mixture having been heated to a temperature in therange from just below the melting point of the soap to about F.'belowthe melting point of the soap, and thereafter cooling the said greasemixture with the addition of the remainder of the lubricating oilcontained in the finished grease at a substantially lower temperaturethan the grease mixture, the improvement which comprises introducing thelubricating oil added during the cooling into a minor recirculatedstream of the grease mixture which is continuously withdrawn from amaintained body of the great mixture and subjecting the combined streamof grease mixture and added lubricating oil to turbulent mixing beforereturning the said combined stream tothe said maintained body of greasemixture, the ratio of the rate of circulation of the grease mixture andthe rate of introducing the said lubricating oil being from about 1:1 toabout 400: 1, respectively., by Weight.

2. The process of claim 1 wherein the said combined stream ofgreasemixture and lubricating oil is passed through a shear valve with apressure drop across the said valve of about 10-200 pounds per squareinch.

3. The process of claim 2 wherein the pressure drop across the saidvalve is about 25 -125 pounds per square inch. 1

4. The process of claim 1 wherein the said grease mixture before coolingcomprises lubricating oil and soap in 'a ratio o f at least :1respectively, by weight.

p 5. The process of claim 1 wherein the said grease mix ture isrecirculated at a rate such that the weight of recirculated greasemixture equals the total average weight of grease mixture in the coolingcycle in about 0.4 27 minutes. t l

6. The process of claim 1 wherein the said soap is chosen from the classconsisting of alkali metal and alkaline earth metal soaps of higherfatty acids and hydroxy fatty acids, and mixtures thereof.

7. The process of claim 1 wherein the said grease is finished bymilling.

1. IN A LOW TEMPERATURE PROCESS FOR PREPARING A SOAP THICKENED GREASEWHICH COMPRISES PROVIDING A HOT GREASE MIXTURE COMPRISING A PORTION OFTHE LUBRICATING OIL CONTAINED IN THE FINISHED GREASE AND SOAP DISPERSEDTHEREIN, SAID GREASE MIXTURE HAVING BEEN HEATED TO A TEMPERATURE IN THERANGE FROM JUST BELOW THE MELTING POINT OF THE SOAP TO ABOUT 75*F. BELOWTHE MELTING POINT OF THE SOAP, AND THEREAFTER COOLING THE SAID GREASEMIXTURE WITH THE ADDITION OF THE REMAINDER OF THE LUBRICATING OILCONTAINED IN THE FINISHED GREASE AT A SUBSTANTIALLY LOWER TEMPERATURETHAN THE GREASE MIXTURE, THE IMPROVEMENT WHCIH COMPRISES INTRODUCING THELUBRICATING OIL ADDED DURING THE COOLING INTO A MINOR RECIRCULATEDSTREAM OF THE GREASE MIXTURE WHICH IS CONTINUOUSLY WITHDRAWN FROM AMAINTAINED BODY OF THE GREAT MIXTURE AND SUBJECTING THE COMBINED STREAMOF GREASE MIXTURE AND ADDED LUBRICATING OIL TO TURBULENT MIXING BEFORERETURNING THE SAID COMBINED STREAM TO THE SAID MAINTAINED BODY OF GREASEMIXTURE, THE RATIO OF THE RATE OF CIRCULATION OF THE GREASE MIXTURE ANDTHE RATE OF INTRODUCING THE SAID LUBRICATING OIL BEING FROM ABOUT 1:1 TOABOUT 400:1, RESPECTIVELY, BY WEIGHT.
 6. THE PROCESS OF CLAIM 1 WHEREINTHE SAID SOAP IS CHOSEN FROM THE CLASS CONSISTING OF ALKALI METAL ANDALKALINE EARTH METAL SOAPS OF HIGHER FATTY ACIDS AND HYDROXY FATTYACIDS, AND MIXTURES THEREOF.